A distance measurement device which is mounted in a vehicle, and for example, projects a laser beam to measure the distance from an object using a time difference until a laser beam reflected from the object is received is hitherto known. If the number of vehicles in which such an object detection device is mounted becomes large, there is an increasing possibility that a laser beam projected by another vehicle is received. In such a case, if a laser beam projected by another vehicle is received immediately after the distance measurement device of the host vehicle projects light, the distance from the object is measured using the time difference; thus, there is a problem in that an erroneous distance is measured.
As a countermeasure for such a problem, for example, JP-A-2006-308482 discloses a detection device which irradiates a target position with a laser beam for preventing erroneous detection in a case where a laser beam from an oncoming vehicle is received, or the like, to detect the situation of the target position. This detection device modulates a pulsed laser beam with a modulation pattern individually set for each target position among several modulation patterns and outputs the pulsed laser beam from a laser emission unit to the target position. Then, it is detected that there is an obstacle at the target position only when the modulation pattern of the pulsed laser beam output from the laser emission unit matches the modulation pattern of the pulsed laser beam received by the laser receiving unit, and the distance from the obstacle is measured. With this, even if a pulsed laser beam is erroneously received from the oncoming vehicle or the like, erroneous detection of the situation of the target position based on the received pulsed laser beam is suppressed.
JP-A-H05-149712 discloses a distance measurement method for an automobile capable of preventing mutual interference in a case where a laser beam is used and reflected light is detected to measure the distance from an object. The distance measurement method for an automobile constitutes an optical signal transmitted from transmission means to have a frame structure with a vehicle code assigned to each vehicle in a head portion, identifies a vehicle code of an optical signal received by receiving means using vehicle code identification means, determines whether the received optical signal is transmitted from the host vehicle or another vehicle, stops the transmission of the optical signal from the host vehicle if the optical signal is transmitted from another vehicle, and transmits the optical signal from the host vehicle after the transmission of the optical signal from another vehicle ends.
JP-A-2013-124941 discloses a distance measurement device which projects a two-dimensional pattern onto a subject to detect the distance to the subject. For example, a circular pattern is projected onto the subject, the diameter of the circle projected onto the subject is detected, and the distance to the subject is measured based on the detection result.